Editing a material without assigning it to the active object
Presently there is no experimental area to create materials before assigning them to an object. This leads to workarounds, and they may be obvious. Ways that come to mind are:


script it, and assign it.
or, create a dummy object like a suzanne (because it's shapely) and create the new material for that and tweak it until satisfied. Then assign the material to the object(s) that you do want to use it with.
or, start a second instance of blender, create suzanne, create a material for it (give it a good name), then save the blend. Then in the original blend go to File > Append > (select file with the material) > Materials > (select the named material) Append . This will append the material to your current .blend file. Assign the new material to the desired object.


Remember, Giving a fake user (the F button) to a material tells blender not to delete that material if it isn't assigned to any objects, when the .blend is saved.

ps. I don't like to use bold letters often, but good names are very handy.